1. Field of the Invention
The present invention relates generally to optical devices and, more specifically, the present invention relates to gain equalization filters.
2. Background Information
The need for fast and efficient optical-based technologies is increasing as the growth rate of Internet data traffic overtakes that of voice traffic, pushing the need for fiber optic communications. Transmission of multiple optical channels over the same fiber in a dense wavelength-division multiplexing (DWDM) system provides a simple way to use the unprecedented capacity (signal bandwidth) offered by fiber optics. Commonly used optical components in the system include wavelength-division multiplexing (WDM) transmitters and receivers, optical add/drop multiplexers, optical filters such as diffraction gratings, thin-film filters, fiber Bragg gratings, arrayed-waveguide gratings and optical amplifiers such as for example erbium-doped fiber amplifiers (EDFAs).
Optical amplifiers such as EDFAs, which typically operate in the C or L wavelength band, are used to amplify optical signals. Applications for EDFAs include amplifying optical beams over for example long distances in optical communications systems. It is well known that the optical gain of an EDFA exhibits strong wavelength dependence. For instance, a known EDFA has a non-uniform spectral response or a non-flat gain spectrum with gain peaks at approximately 1530 due to amplified spontaneous emission and 1560 nanometers. The non-uniform spectral response of optical amplifiers such as EDFAs presents complexities in optical applications such as transparent DWDM lightwave networks, where multiple channels over a spectrum of wavelengths are included in optical beams. Consequently, different channels in the DWDM lightwave networks are amplified with different optical gain. Another challenge associated with known EDFAs is that the non-uniform spectral response of the output is varied as a function of the optical power of the input optical signal to the EDFA. The problems associated with the non-uniform spectral response of EDFAs are further exacerbated when multiple EDFAs are cascaded. Known solutions to equalize the gain of EDFAs are complicated and typically utilize complex multiple-cavity bandpass Fabry-Perot (FP) filters over the entire C-band (e.g. 1530 to 1565 nanometers).